C# quickest way to shift array

How can I quickly shift all the items in an array one to the left, padding the end with null?

For example, [0,1,2,3,4,5,6] would become [1,2,3,4,5,6,null]

Edit: I said quickly but I guess I meant efficiently. I need to do this without creating a List or some other data structure. This is something I need to do several hundred thousand times in as short amount of time as possible.